Liquid Crystal Display Device

ABSTRACT

A counter voltage supply circuit has an inverting amplifier that inversely amplified a voltage detected from a specified part of a counter electrode of a liquid crystal display panel and supplies the amplified voltage to a counter voltage supply end of the counter electrode. The inverting amplifier includes an operational amplifier having a feedback resistor connected between an inverting input terminal and an output terminal. The feedback resistor includes a first resistor, and n resistors each of which is connected parallel to the first resistor via a switching element. As the n switching elements are selectively turned on and off by a switching element control circuit in accordance with a scanning position, the resistance value of the feedback resistor is varied and the gain of the operational amplifier is changed. Cross-talk due to coupling noise to the counter electrode generated by AC driving of a video voltage and deterioration in display quantity of a display image on the liquid crystal display panel can be prevented.

The present application claims priority from Japanese applicationJP2007-153438 filed on Jun. 11, 2007, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device andparticularly to a liquid crystal display device in which a voltagechange in a counter electrode of a large-size high-definition liquidcrystal display panel is corrected.

2. Description of the Related Art

Recently, liquid crystal display modules have been broadly used forsmall-size display devices to display devices for OA equipment,large-size television and so on. In the liquid crystal display module, alayer of liquid crystal composite (liquid crystal layer) is held betweena pair of insulating substrates, at least one of which is basically madeof a transparent glass board, plastic substrate and so on, and a liquidcrystal display panel is thus formed.

Particularly, a liquid crystal display module of a TFT system using athin film transistor as an active element can display a high-definitionimage and is therefore used as a display device of a television orpersonal computer display and so on.

Generally, an active-matrix liquid crystal display device employs alongitudinal electric field system in which an electric field to changethe orientation of the liquid crystal layer is applied between anelectrode formed on one substrate and an electrode formed on the othersubstrate. Moreover, a liquid crystal display module in which thedirection of an electric field applied to the liquid crystal layer issubstantially parallel to the substrate surface (this is referred to asa lateral electric field system or in-plane switching (IPS) system) hasbeen practically used.

In this liquid crystal display panel, in an area surrounded by twoneighboring scanning lines (also referred to as gate lines) and twoneighboring video lines (also referred to as source lines or drainlines), a thin film transistor that turns on when a selective scanningsignal from a scanning line is inputted, and a pixel electrode suppliedwith a video signal from a video line via the thin film transistor areformed, thus constituting a so-called subpixel.

The plural video lines are supplied with a video voltage (gray scalevoltage) from a drain driver arranged in a peripheral part of the liquidcrystal display panel. The plural scanning lines are supplied with aselective scanning voltage from a gate driver arranged in the peripheralpart of the liquid crystal display panel.

As a direct current (DC) is applied to liquid crystal for a long time,the life of the liquid crystal is reduced. Therefore, so-called ACdriving is typically carried out in which a video voltage inputted tothe pixel electrode of each subpixel is changed to a higher potentialthan the counter voltage inputted to the counter electrode or to a lowerpotential than the counter voltage inputted to the counter electrode ina predetermined cycle.

In the active-matrix liquid crystal display module, as the panel hashigher definition, the absolute number of video lines increases andcoupling noise to the counter electrode at the time of voltage change inthe video lines in AC driving increases.

Also, as the liquid crystal panel increases in size, the resistancecomponent from a counter voltage supply source that supplies a countervoltage to the counter electrode cannot be ignored and a problem arisesthat there a greater difference in coupling noise due to change in thevideo lines between the near end and far end of the counter voltagesupply source.

To deal with this problem, there has been known a technique of supplyingthe counter electrode with an inverting signal of a voltage change inthe counter electrode detected from a specified part, as disclosed inJP-A-6-186530.

However, simply supplying the counter electrode with an inverting signalof a voltage change in the counter electrode detected from a specifiedpart, as disclosed in JP-A-6-186530, not only causes occurrence ofchrominance non-uniformity on the liquid crystal display panel that isdependent on the distance from the counter voltage supply source, butalso causes deterioration in image quality due to cross-talk and so on.

SUMMARY OF THE INVENTION

In view of the foregoing circumstances, it is an object of the presentinvention to prevent cross-talk due to coupling noise to the counterelectrode generated in AC driving of a video voltage in the liquidcrystal display panel, and to prevent deterioration in display qualityof a displayed image on the liquid crystal display panel.

The above and other objects and additional features of the inventionwill become clear in the description of this specification and theattached drawings.

Typical examples the invention disclosed in the present application andtheir outlines will be briefly described hereinafter.

(1) A liquid crystal display device according to an aspect of theinvention includes a liquid crystal display panel having pluralsubpixels and plural scanning lines that input a selective scanningvoltage to the plural subpixels, and a scanning line driving circuitthat sequentially supplies the selective scanning voltage to the pluralscanning lines. Each of the plural subpixels has a counter electrode. Acounter voltage supply circuit that supplies a counter voltage to thecounter electrode is provided. The counter voltage supply circuit has aninverting amplifier that inversely amplifies a voltage detected from aspecified part of the counter electrode of the liquid crystal displaypanel and supplies the voltage to a counter voltage supply end of thecounter electrode. The inverting amplifier includes an operationalamplifier having a feedback resistor that is connected between aninverting input terminal and an output terminal. The feedback resistorhas n resistors and n switching elements that insert the n resistorsinto a feedback route of the operational amplifier or take out the nresistors from the feedback route of the operational amplifier. Aswitching element control circuit is provided that selectively turns onand off the n switching elements so as to vary resistance value of thefeedback resistor and thus changes a gain of the operational amplifierin accordance with the position of the scanning lines to which thescanning line driving circuit supplies the selective scanning voltage.

(2) In the device of (1), as spacing between the counter voltage supplyend and each of the plural scanning lines increases, the gain of theoperational amplifier increases.

(3) In the device of (1), the plural scanning lines are divided intoplural groups and the gain of the operational amplifier changes for eachscanning line of each of the groups.

(4) In the device of (1), the feedback resistor includes a firstresistor, and n resistors each of which is connected parallel to thefirst resistor via the switching element.

(5) In the device of (1), the feedback resister includes a firstresistor, n resistors connected in series to the first resistor, and then switching elements connected parallel to the n resistors.

(6) In the device of (1), when each of resistance values of the nresistors is expressed as R1, R2, . . . , Rn, the relation ofRn=2^((n-1))×R1 is satisfied.

(7) In the device of (1), the liquid crystal display panel has pluralvideo lines that input a video voltage to the plural subpixels. A videoline driving circuit that supplies a video voltage to the plural videolines is provided. The counter voltage supply end of the counterelectrode is an end close to the video line driving circuit, of thecounter electrode. The specified part of the liquid crystal displaypanel is an end that is farthest from the video line driving circuit, ofthe counter electrode.

The advantages of the typical examples of the invention disclosed inthis application will be briefly described as follows.

According to the invention, in a large-size high-definition liquidcrystal display panel, it is possible to prevent cross-talk due tocoupling noise to the counter electrode generated in AC driving of avideo voltage, and to prevent deterioration in display quality of adisplayed image on the liquid crystal display panel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic configuration of a liquid crystal displaymodule according to an embodiment of the invention.

FIG. 2 is a circuit diagram showing an equivalent circuit of a liquidcrystal display panel 1 shown in FIG. 1.

FIG. 3 is a view for explaining the capacity of one subpixel.

FIG. 4 is a schematic view for explaining the state where a counterelectrode received coupling by a parasitic capacitance in accordancewith a voltage change in a video line.

FIG. 5 is a view showing a counter voltage correcting circuit for acounter electrode described in JP-A-6-186530.

FIG. 6-1 is a circuit diagram showing an exemplary inverting amplifieraccording an embodiment of the invention.

FIG. 6-2 is a circuit diagram showing an exemplary inverting amplifieraccording an embodiment of the invention.

FIG. 7 is a timing chart showing an example of on-off timing ofswitching elements of FIG. 6.

FIG. 8 is a graph showing an exemplary relation between the resistancevalue of a feedback resistor of an inverting amplifier including anoperational amplifier shown in FIG. 6 and the position of a displayline.

FIG. 9 shows a display pattern in which cross-talk tends to occur.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the invention will be described in detailwith reference to the drawings.

In all the drawings for explaining the embodiment, parts and unitshaving the same functions are denoted by the same reference numerals andtheir description will be repeated.

FIG. 1 shows a schematic configuration of a liquid crystal displaymodule according to an embodiment of the invention. FIG. 2 is a circuitdiagram showing an equivalent circuit of a liquid crystal display panel1 shown in FIG. 1.

The liquid crystal display module of this embodiment includes the liquidcrystal display panel 1, a drain driver 2, a gate driver 3, a displaycontrol circuit 4, and a power supply circuit (not shown).

The liquid crystal display module of this embodiment has a countervoltage detection terminal (TVcom), an inverting amplifier (AMP), and aswitching element control circuit (SCTL), as a pixelposition-corresponding counter voltage correcting circuit.

The drain driver 2 and the gate driver 3 are installed in peripheralparts of the display panel 1. For example, the drain driver 2 and thegate driver 3 are mounted respectively by a COG method in peripheralparts on two sides of a first substrate of a pair of substrates (forexample, glass boards) of the liquid crystal display panel 1.Alternatively, the drain driver 2 and the gate driver 3 are mountedrespectively by a COF method on flexible circuit boards arranged inperipheral parts on two sides of the first substrate of the liquidcrystal display panel 1.

The display control circuit 4 and the power supply circuit are mountedrespectively on circuit boards arranged in peripheral parts of theliquid crystal display panel 1 (for example, the back side of the liquidcrystal display module) The power supply circuit generates variousvoltages required for the liquid crystal display device.

The display control circuit 4 carries out timing adjustment suitable fordisplay on the liquid crystal display panel 1, such as AC conversion ofdata, of a display control signal (CTS) and display data (Din) inputtedfrom a display signal source (host side) like a personal computer ortelevision receiving circuit, converts the data into display dataaccording to a display format, and inputs the data to the drain driver 2and the gate driver 3 together with a synchronizing signal (clocksignal).

The gate driver 3 sequentially supplies a selective scanning voltage toscanning lines (also referred to as gate lines (GL)) under the controlof the display control circuit 4. The drain driver 2 supplies a videovoltage to video lines (also referred to as drain lines and source lines(DL)) to display a video.

As shown in FIG. 2, the liquid crystal display panel 1 has pluralsubpixels. Each subpixel is provided in an area surrounded by videolines (DL) and scanning lines (GL).

Each subpixel has a thin film transistor (TFT). A first electrode (drainelectrode or source electrode) of the thin film transistor (TFT) isconnected to a video line (DL). A second electrode (source electrode ordrain electrode) of the thin film transistor (TFT) is connected to apixel electrode (PX). The gate electrode of the thin film transistor(TFT) is connected to a scanning line (GL).

In FIG. 2, LC represents liquid crystal capacitance equivalently showinga liquid crystal layer arranged between a pixel electrode (PX) and acounter electrode (CT). Cst represents a retention capacitance formedbetween a pixel electrode (PC) and a counter electrode (CT).

In the liquid crystal display panel 1 shown in FIG. 1, the firstelectrode of the thin film transistor (TFT) of each subpixel arranged inthe direction of column is connected to a video line (DL), and eachvideo line (DL) connects the drain driver 2 that supplies a videovoltage (gray scale voltage) corresponding to display data, to thesubpixels arranged in the direction of column.

The gate electrode of the thin film transistor (TFT) of each subpixelarranged in the direction of row is connected to a scanning line (GL),and each scanning line (GL) is connected to the gate driver 3 thatsupplies a scanning voltage (positive or negative bias voltage) to thegate of the thin film transistor (TFT) for one horizontal scanning time.

The display control circuit 4 includes one semiconductor integratedcircuit (LSI) and controls and drives the drain driver 2 and the gatedriver 3 in accordance with externally inputted various display controlsignals including dot clock (DCLK), display timing signal (DTMG),external horizontal synchronizing signal (Hsync) and external verticalsynchronizing signal (Vsync), and display data.

When a display timing signal (DTMG) is inputted, the display controlcircuit 4 determines this as a display start position and outputs areceived simple column of display data to the drain driver 2 via adisplay data bus line.

At this time, the display control circuit 4 outputs a display data latchclock signal (CL2), which is a display control signal for latchingdisplay data, to a data latch circuit of the drain driver 2 via a signalline.

When the input of the display timing signal (DTMG) has been finished ora predetermined time has passed since the input of the display timingsignal (DTMG), the display control circuit 4 assumes that one horizontalline of display data has been finished, and outputs an output timingcontrol clock signal (CL1), which is a display control signal foroutputting the display data stored in the latch circuit of the draindriver 2 to a video line (DL) of the liquid crystal display panel 1, tothe drain driver 2 via a signal line. Thus, the drain driver 2 suppliesa video voltage corresponding to the display data to the video lines(DL).

As the first display timing signal is inputted after the input of avertical synchronizing signal, the display control circuit 4 determinesthis as the first display line and outputs a frame start designatingsignal (FLM) to the gate driver 3 via a signal line.

Moreover, in accordance with a horizontal synchronizing signal, thedisplay control circuit 4 outputs a shift clock (CL3) of one horizontalscanning time cycle to the gate driver 3 via a signal line so that aselective scanning voltage (positive bias voltage) is sequentiallysupplied to each scanning line (GL) of the liquid crystal display panel1, everyone horizontal scanning time.

Thus, the plural thin film transistors (TFT) connected to each scanningline (GL) of the liquid crystal display panel 1 are electricallyconnected for one horizontal scanning time.

The voltage supplied to the video lines (DL) is applied to pixelelectrodes (PX) via the thin film transistors (TFT), which areelectrically connected for one horizontal scanning time. Eventually, asthe retention capacitances (Cst) and the liquid crystal capacitances(LC) are electrically charged to control the liquid crystal molecules,an image is displayed.

The liquid crystal display panel 1 is formed by superimposing, with apredetermined spacing, the first substrate on which the pixel electrodes(PX), thin film transistors (TFT) and so on are formed and the secondsubstrate on which a color filter and so on are formed, then bonding thetwo substrates with a sealant provided in the shape of a frame nearperipheral edges between the two substrates, then filling the spaceinside of the sealant between the two substrates with liquid crystalfrom a liquid crystal encapsulation port provided at a part of thesealant and encapsulating the liquid crystal, and then bonding apolarizer onto the outside of the two substrates.

The counter electrodes (CT) are provided on the second substrate if itis a liquid crystal display panel of the TN system or VA system. In thecase of the IPS system, the counter electrodes (CT) are provided on thefirst substrate.

Since the present invention is not related to the internal structure ofthe liquid crystal panel, the detailed description of the internalstructure of the liquid crystal panel is omitted. Moreover, the presentinvention can be applied to a liquid crystal panel of any structure.

The counter electrodes (CT) are connected to have the same potential inthe entire liquid crystal display panel. A voltage from the invertingamplifier (AMP) is supplied to the counter electrodes (CT) of the liquidcrystal display panel via the drain driver circuit board, as indicatedby A2 in FIG. 1.

In this embodiment, in order to correct a change at the counterelectrodes (CT) due to a voltage change in the video lines (DL), thecounter voltage detection terminal (TVcom) is provided at the farthestend from the counter voltage supply point of the counter electrodes(CT), and a voltage (A1 in FIG. 1) detected by this counter voltagedetection terminal (TVcom) is inputted to the inverting amplifier (AMP).

The inverting amplifier (AMP) includes an operational amplifier, as willbe described later. The gain of the inverting amplifier (AMP) changed inaccordance with the display line position.

FIG. 3 is a view for explaining a part that constitutes the capacitanceof one subpixel. In FIG. 3, LC represents the liquid crystal capacitanceof the subpixel, Cdc represents the parasitic capacitance between thevideo line and the counter electrode, Cgc represents the parasiticcapacitance between the scanning line and the counter electrode, and Cgdrepresents the parasitic capacitance between the scanning line and thevideo line.

FIG. 4 is a schematic view for explaining the state where the counterelectrode (CT) receives coupling by the parasitic capacitance inaccordance with voltage change in the video lines (DL).

The video lines (DL) are typically set in such a manner that thevoltages of two neighboring video lines (DL) are driven in oppositepolarities in order to reduce flicker. In FIG. 4, DLV(+) represents apositive video voltage of the video lines (DL), and DLV(−) represents anegative video voltage of the video lines (DL). GLV represents aselective scanning voltage of the scanning lines (GL).

As described above, the video voltage inputted to the video lines (DL)has its polarity inverted with respect to the counter voltage (Vcom) ofthe counter electrode (CT) in a predetermined cycle in order to preventapplication of a direct current (DC) to the liquid crystal.

However, when a specified pattern is displayed, the video voltage of onepolarity inputted to the video lines (DL) increases and the potential ofthe counter electrode (CT) changes because of the coupling by theparasitic capacitance, as indicated by A3 in FIG. 4.

After that, as the counter voltage (Vcom) is supplied from the countervoltage supply circuit (here, the inverting amplifier (AMP)), thevoltage of the counter electrode (CT) returns to the original countervoltage (Vcom). However, in the case where the original counter voltage(Vcom) cannot be restored before the scanning lines (GL) turn off, adifferent voltage from the voltage that should be originally written iswritten to the liquid crystal capacitance (LC). This is a writing errorand deteriorates the display quality.

In a relatively small liquid crystal display panel, since the area ofthe counter electrode (CT) is small, the original potential is easilyrestored even when there is a change in the counter electrode (CT), andthe display quality is less likely to deteriorate. However, in ahigh-definition panel, as the number of video lines (DL) increases, theinfluence of the parasitic capacitance (Cdc) between the video line andthe counter electrode, and of the parasitic capacitance (Cgc) betweenthe scanning line and the counter electrode through the parasiticcapacitance (Cgd) between the scanning line and the video lineincreases.

Also, recently, as the frame refresh rate of the liquid crystal displaypanel 1, double-speed or triple-speed driving is carried out to supportdynamic images, and the on-time of the gate is increasingly reduced.Since the time required for the counter electrode (CT) having a voltagechange to restore the original counter voltage (Vcom) is insufficient, awriting error occurs and deterioration in image quality such ascross-talk become prominent.

FIG. 5 is a view showing the counter voltage correcting circuit of thecounter electrode (CT) described in JP-A-6-186530. In the countervoltage correcting circuit of the counter electrode (CT) described inJP-A-6-186530, a voltage change in the counter electrode (CT) detectedby a sensing line 20 is inputted to an inverting circuit 21, and thisinversion signal is supplied to the counter electrode (CT).

In the liquid crystal display device described in JP-A-6-186530,measures for the supply to the counter electrode (CT) of the liquidcrystal display panel are taken such as providing a supply line on theoutermost periphery of the liquid crystal display panel. However, sincethis increases the size of the liquid crystal display panel itself, theresistance component in the liquid crystal display panel cannot beignored and the time constant difference at the time of supplying thecounter voltage expands between a part close to the counter voltagesupply end and the far end. Therefore, for example, in the case wherethe voltage of the counter electrode (CT) located at the farthestposition from the counter voltage supply end of the liquid crystaldisplay panel is detected and corrected, this correction turns out to beexcessive on the side close to the counter voltage supply end of theliquid crystal display panel, but the correction is insufficient on thefar end side because of the resistance component in the liquid crystaldisplay panel.

However, in the case of the counter voltage correcting circuit accordingto this embodiment, while the detected voltage is amplified by theinverting amplifier (AMP) and then supplied to the counter electrode(CT), the gain of the inverting amplifier (AMP) is set on the basis ofthe distance between the scanning line (GL) that is now being scannedand the counter voltage supply end in consideration of the resistancecomponent in the liquid crystal display panel. Therefore, uniformcorrection can be made in the liquid crystal display panel.

Hereinafter, a specific example of this embodiment will be described.

As shown in FIG. 1, the counter voltage (Vcom) is generated in theperipheral circuit and is supplied to the counter electrode (CT) of theliquid crystal display panel 1 via the low-resistance video line drivingcircuit board. In the case of FIG. 1, the top part of the liquid crystaldisplay panel is close to the counter voltage supply end and the bottompart of the liquid crystal display panel is the far end side from thecounter voltage supply end.

The counter electrode (CT) is influenced by AC driving of the videolines (DL) via the liquid crystal capacitance (LC) and each parasiticcapacitance (Cdc, Cgc, Cgd). Its quantity is defined by the differencein quantity of variance to positive polarity or negative polarity of thevideo lines (DL) on one display line.

FIG. 9 shows a display pattern in which cross-talk tends to occur.Generally, one pixel in the panel of the liquid crystal display moduleincludes a set of subpixels of three primary colors R, G and B. Pixelsare arranged in a repeated manner in order of the subpixels of R, G andB. A video line (DL) and a liquid crystal capacitance (LC) are connectedto each of the subpixels of R, G and B, and a video voltage, which isimage information, is supplied thereto from the drain driver 2.

Generally, video voltages supplied to neighboring video lines (DL) areset to have opposite polarities. For example, in the case of normallyblack liquid crystal, at the time of white display, a maximum videovoltage of positive polarity (POT) is applied to the R and B subpixelsand a maximum video voltage of negative polarity (NEG) is applied to theG subpixel. In the case where this is repeated, that is, in the casewhere white and black are alternately displayed by each pixel, thenumber of G video lines (DL) supplied with the negative-polarity videovoltage is half the number of R and B video lines (DL) supplied with thepositive-polarity video voltage in one line. Because of coupling due tovoltage change in the video lines (DL), the voltage of the counterelectrode (CT) shifts to positive polarity, as indicated by A in FIG. 9.

In this state, in the case where the scanning lines (GL) are off, thatis, where writing of the voltage to the liquid crystal capacitance (LC)has been finished, a relatively high voltage has been written only tothe G subpixel, compared to the supplied video voltage. Thus, whiteshifts to green. Moreover, in the area where medium tone (MRA) is shownon the same display line, contrast occurs by each one pixel and aphenomenon of deterioration in image quality called cross-talk isobserved.

In this embodiment, to overcome the deterioration in image quality dueto the change in the counter voltage, a corrected voltage correspondingto the display line position of the liquid crystal display panel isprovided to the counter electrode (CT) by a pixel position-correspondingcounter voltage correcting circuit.

FIG. 6-1 is a circuit diagram showing an example of the invertingamplifier according to this embodiment. FIG. 6-1 shows an invertingamplifier using an operational amplifier (OP). A buffer circuit (BA)including a bipolar transistor is connected to the output terminal ofthe operational amplifier (OP). A feedback resistor is connected betweenthe inverting input terminal (−) and the output terminal of theoperational amplifier (OP). This feedback resistor includes a resistorRa and a parallel circuit of resistors R1 to R4.

The inverting amplifier shown in FIG. 6-1 inversely amplifies a voltage(VcomS) from the counter voltage detection terminal (TVcom) on thebottom part of the liquid crystal display panel, provided at thefarthest end from the counter voltage supply end of the liquid crystaldisplay panel 1, and supplies the amplified voltage (VcomOut) to thecounter electrode (CT) as the counter voltage (Vcom). In FIG. 6-1,VcomIn represents the original counter voltage (Vcom).

In this case, when the scanning lines (GL) on the top part of the liquidcrystal display panel, which is close to the counter voltage supply end,are being scanned, the gain of the inverting amplifier is lowered toprevent excessive correction. When the scanning lines (GL) on the bottompart of the liquid crystal display panel, which is the far end, arebeing scanned, the gain is raised in consideration of the resistancecomponent in the liquid crystal display panel, thus compensating for theinsufficient correction.

In this embodiment, as a method of changing the gain of the invertingamplifier in accordance with this scanning, the feedback resistance ofthe inverting amplifier including the operational amplifier (OP) isvaried. To this end, in this embodiment, the resistors 11 to 14 areconnected parallel to the resistor Ra via switching elements (SW1 toSW4), as shown in FIG. 6-1, and the switching elements (SW1 to SW4) areselectively turned on and off by a switching element control circuit(SCTL). Thus, the feedback resistance is varied.

Here, when the resistance value of the resistor 11 is R1, the resistancevalue R2 of the resistor 12 is R2=2⁽²⁻¹⁾ ⁾×R1, the resistance value R3of the resistor 13 is R3=4(2⁽³⁻¹⁾×R1, and the resistance value R4 of theresistor 14 is R4=8(2⁽⁴⁻¹⁾×R1. That is, the resistors 11 to 14 areweighted.

In the case where n resistors (in FIG. 6-1, four resistors 11 to 14) areconnected to the resistor Ra, in this embodiment, when the feedbackresistance of the operational amplifier (OP) is varied in accordancewith scanning, all the scanning lines are divided into 2 ^(n) (in FIG.6-1, 2⁴=16) groups and the feedback resistance of the operationalamplifier (OP) is varied by each of the divided groups.

Therefore, the switching element control circuit (SCTL) has an innercounter to count the inputted shift clock (CL3), determines which groupthe scanned scanning line (GL) belongs to in accordance with the countvalue of the counter, and selectively turns on and off the switchingelements (SW1 to SW4) in accordance with switching element controlsignals (SSW1 to SSW4).

Reset in FIG. 6-1 represents a signal synchronized with the verticalsynchronizing signal (Vsync) (or the vertical synchronizing signal(Vsync)). This signal is for resetting the inner counter.

FIG. 7 shows an example of on-off timing of the switching elements (SW1to SW4). FIG. 8 shows an example of the relation between the resistancevalue of the feedback resistor of the inverting amplifier including theoperational amplifier and the display line position in this case. InFIG. 7 and FIG. 8, HLNo represents the display line position andcorresponds to the scanning lines of each of the 16 divided groups.

Generally, the gain of the inverting amplifier including the operationalamplifier (OP) is expressed by (−Ra/Rb) Therefore, in the case where theresistance value of the feedback resistor changes as shown in FIG. 8,the gain of the inverting amplifier including the operational amplifier(OP) changes in the same manner as shown in FIG. 8. Thus, when thescanning lines (GL) on the top part of the liquid crystal display panel,which is close to the counter voltage supply end, are being scanned, thegain of the inverting amplifier can be lowered, whereas when thescanning lines (GL) on the bottom part of the liquid crystal displaypanel, which is the far end, are being scanned, the gain can be raisedin consideration of the resistance component in the liquid crystaldisplay panel.

FIG. 6-2 is a circuit diagram showing another example of the invertingamplifier according to this embodiment. The inverting amplifier shown inFIG. 6-2 is different from the inverting amplifier shown in FIG. 6-1 inthat the resistors 11 to 14 are connected in series to the resistor Raand that the switching elements (SW1 to SW4) of the resistors 11 to 14are connected in parallel.

Also in the inverting amplifier shown in FIG. 6-2, the feedbackresistance can be varied as the switching elements (SW1 to SW4) areselectively turned on and off by the switching element control circuit(SCTL). In FIG. 6-1 and FIG. 6-2, the resistors connected in series orparallel to the resistor (Ra) are not limited to four resistors. Two,three, or six or more resistors can be connected.

As described above, in this embodiment, in the liquid crystal displaypanel (particularly a large-size high-definition liquid crystal displaypanel), a change in the counter voltage (Vcom) due to AC driving of thevideo lines (DL) is corrected in accordance with the distance from thecounter voltage supply end. Therefore, deterioration in image qualitydue to insufficient writing caused by coupling noise to the counterelectrode (CT) generated by AC driving of the video lines (DL), ordeterioration in image quality due to the cross-talk phenomenon on theentire surface of the liquid crystal display panel can be solved.

The invention made by the present inventor has been specificallydescribed with reference to the embodiment. However, the presentinvention should not be limited to the embodiment and various changesand modifications can be made without departing from the scope of theinvention.

1. A liquid crystal display device comprising: a liquid crystal displaypanel having plural subpixels and plural scanning lines that input aselective scanning voltage to the plural subpixels; and a scanning linedriving circuit that sequentially supplies the selective scanningvoltage to the plural scanning lines; each of the plural subpixelshaving a counter electrode; the device having a counter voltage supplycircuit that supplies a counter voltage to the counter electrode; andthe counter voltage supply circuit having an inverting amplifier thatinversely amplifies a voltage detected from a specified part of thecounter electrode of the liquid crystal display panel and supplies thevoltage to a counter voltage supply end of the counter electrode;wherein the inverting amplifier includes an operational amplifier havinga feedback resistor that is connected between an inverting inputterminal and an output terminal; the feedback resistor has n resistorsand n switching elements that insert the n resistors into a feedbackroute of the operational amplifier or take out the n resistors from thefeedback route of the operational amplifier; and a switching elementcontrol circuit is provided that selectively turns on and off the nswitching elements so as to vary resistance value of the feedbackresistor and thus changes a gain of the operational amplifier inaccordance with the position of the scanning lines to which the scanningline driving circuit supplies the selective scanning voltage.
 2. Theliquid crystal display device according to claim 1, wherein as spacingbetween the counter voltage supply end and each of the plural scanninglines increases, the gain of the operational amplifier increases.
 3. Theliquid crystal display device according to claim 1, wherein the pluralscanning lines are divided into plural groups and the gain of theoperational amplifier changes for each scanning line of each of thegroups.
 4. The liquid crystal display device according to claim 1,wherein the feedback resistor includes a first resistor, and n resistorseach of which is connected parallel to the first resistor via theswitching element.
 5. The liquid crystal display device according toclaim 1, wherein the feedback resister includes a first resistor, nresistors connected in series to the first resistor, and the n switchingelements connected parallel to the n resistors.
 6. The liquid crystaldisplay device according to claim 1, wherein when each of resistancevalues of the n resistors is expressed as R1, R2, . . . , Rn, therelation of R=2^((n-1))×R1 is satisfied.
 7. The liquid crystal displaydevice according to claim 1, wherein the liquid crystal display panelhas plural video lines that input a video voltage to the pluralsubpixels, the device has a video line driving circuit that supplies avideo voltage to the plural video lines, the counter voltage supply endof the counter electrode is an end close to the video line drivingcircuit, of the counter electrode, and the specified part of the liquidcrystal display panel is an end that is farthest from the video linedriving circuit, of the counter electrode.